低流量下阵列式微通道对流沸腾特性实验研究

Experimental study of convective boiling characteristics at low mass flow rates in a micro-channel array heat sink

设计了阵列式微通道热沉结构,进行了并R134a的沸腾流动换热实验。结果证明,在低干度区域由泡状流/弹状流/半环状流主导,主导换热机理为对流沸腾和蒸发,热交换系数随热流密度显著增加,随质量流量增大而略有增加。在高干度区域搅拌流/束状流主导沸腾流动,对流蒸发为主导换热机理,换热系数随流量增大而增大。该结构可以在低流量下提前紊流转捩;有效抑制压力波动,减小进出口压力差。实验观察发现搅拌流/束状流型,气液界面波失稳导致液膜破碎和卷携。液滴沉积会润湿局部蒸干壁面。当热流持续增大,液膜破碎并大量被卷携入气核后,壁面附着气膜且无法被润湿,形成反束状流型时,触发CHF。

An array structure was used in micro-channel heat sink design and the boiling flow experi- ments of R134a were conducted. The test results demonstrat that at low vapor qualities, the flow patterns were bubbly/slug/semi-annular flow, where the boiling flow was dominated by convective boiling and evap- oration ; the heat transfer coefficients increased significantly with the heat flux and slightly rose with the mass flow rates. At the high vapor qualities, the flow patterns were wispy/churn flow, where the boiling flow was dominated by convective evaporation and the heat transfer coefficients increased with the mass flow rates. This array structure could advance the transition from laminar to turbulent flow, depress the pressure fluctuations and decrease the pressure drop. In churn/wispy flow, the instability of vapor-liquid interracial wave caused the liquid film breakup and entrainment; the liquid drops deposit at the wall could rewet the dry-out region. When the heat flux increased enough, a lot of breakup liquid film was entrained into the vapor core, the vapor blankets covered the wall and the dry-out region could not be rewetted; therefore the reverse wispy flow appeared, which initiated the CHF.